Pasteurisation: Pasteur's greatest contribution to health
Authors: Russell Currier
Journal: The Lancet Microbe (2022)

December, 2022, marks the 200th year of Louis Pasteur's birth in Dole, France. Among Pasteur's major contributions and their benefit to society, the most important is the heat treatment of foods and beverages to reduce spoilage and eliminate pathogens for consumers. This process became known as pasteurisation while Pasteur was still alive.1Dubos R Louis Pasteur: free lance of science. Little, Brown and Company, Boston, MA1950Google Scholar After obtaining a doctorate degree in chemistry, Pasteur began studying crystallography—a field of intense activity at the time. He spent about a decade (1847–57) investigating the ability of organic substances to rotate a plane of polarised light. In retrospect, this action's value was muted and not of great consequence in the fields of medicine and health.2Geison GL The private science of Louis Pasteur. Princeton University Press, Princeton, NJ1995Google Scholar The next phase of his research (1857–65) was on fermentation, helping to dispel the notion of spontaneous generation—ie, that microbes and, hence spoilage or fermentation, arose spontaneously. This work was followed by studies on vinegar and wine where Pasteur advanced the concept of heat treatment, not for complete sterilisation, but to effect reduction of microbial flora.2Geison GL The private science of Louis Pasteur. Princeton University Press, Princeton, NJ1995Google Scholar About that time (1865–70), silkworms (silk production being a major industry in France) began to be affected by two diseases: pébrine and muscardine. Pasteur's reputation prompted French authorities and industry officials to invite him to study and identify methods to address the problems (note that Pasteur did not know anything about silkworms). Ultimately, the cause of pébrine was assigned to a protozoon called Nosema bombycis. The cause of muscardine was established as fungal, specifically caused by Beauveria bassiana. Most importantly, he worked out a strategy to eliminate the pests through careful screening of breeding stock, since pébrine can be transferred both vertically and horizontally. This research enabled Pasteur to make a connection between microbial life and disease.1Dubos R Louis Pasteur: free lance of science. Little, Brown and Company, Boston, MA1950Google Scholar In subsequent years (1871–76), silkworm studies were followed by a return to dealing with beer production issues and defending his views on spontaneous generation and fermentation. Pasteur became a recognised authority on industrial fermentation and, in the process, was invited into the Whitbread Breweries in Britain and Carlsberg in Denmark to investigate fermentation. These breweries attribute their success to Pasteur's identification of the contaminating microorganism.3Cavaillon JM Legout S Louis Pasteur: between myth and reality.Biomolecules. 2022; 12: 596Crossref PubMed Scopus (6) Google Scholar Pasteur spent the final years of his career (1877–95) developing vaccines for livestock, particularly for anthrax, fowl cholera, and swine erysipelas. A few of these breakthroughs were serendipitous and several were advanced by colleagues without acknowledgment by Pasteur. Pasteur also wanted to develop a vaccine for humans and completed this phase of his career working on rabies, using dogs and rabbits as experimental models. His ultimate triumph was the vaccination of Joseph Meister who, at age 9 years, had several severe bites from a "mad" presumably rabid dog. Young Meister survived and, in adulthood, became a guard for Pasteur's tomb at the Pasteur Institute. Tragically, he died by suicide in World War 2, after Nazi soldiers forced him to enable access to Pasteur's remains.1Dubos R Louis Pasteur: free lance of science. Little, Brown and Company, Boston, MA1950Google Scholar, 2Geison GL The private science of Louis Pasteur. Princeton University Press, Princeton, NJ1995Google Scholar, 4Williams E The forgotten giants behind Louis Pasteur: contributions by the veterinarians Toussaint and Galtier.Vet Herit. 2010; 33: 33-39PubMed Google Scholar Probably the greatest achievement of Pasteur was the process that bears the name of this famous scientist who perfected the technique: pasteurisation. For liquids, this process does not involve boiling the product to sterility but simply applying just enough heat (ie, par-boiling) to 50–60°C for a specified period to reduce spoilage microbes and potential pathogens. Pathogenic microbes have a lower heat tolerance than most other bacteria. Recognising that many individuals, from the highly educated to the peasantry, were aware of the effect, it took someone like Pasteur to formalise this knowledge into specific time-temperature standards to assure consistency. Needless to say, when new technology evolves there can be a natural reluctance to subscribe to it. However, Pasteur who was well aware of this problem often employed public demonstrations of the recommended technique or procedure. As an experiment, a batch of wine was heated and then sent to sea along with some unheated product on a vessel named Jean Bart. On return 10 months later, the heated wine was found to be very satisfactory whereas the unheated wine was organoleptically bad with "an astringent, almost acid flavor".5Vallery-Radot R Devonshire RL The life of Pasteur. Garden City Publishing, Garden City1937Google Scholar To convince more skeptics, Pasteur personally supervised the French Navy frigate La Sibylle to carry a complete cargo of heated wine on a circumnavigation of the world that arrived back "unspoilt".5Vallery-Radot R Devonshire RL The life of Pasteur. Garden City Publishing, Garden City1937Google Scholar This effort helped enable the protection of the French wine and beer industries. Remarkably, this same technology was successfully applied to milk in 1886 by German chemist, Franz von Soxhlet. Milk-borne infections had a long history of fatally infecting children and infants. Subsequently, Danish authorities picked up on this useful technique, including pasteurisation on an industrial scale, and demonstrated its enormous value. In the ensuing decades, problems and concerns were addressed in pasteurisation, resulting in worldwide acceptance and use of the process for most commercial milk by the late 1920s.7Frederiksen JD The story of milk. Macmillan Company, New York, NY1910Google Scholar, 8Currier RW Widness JA A brief history of milk hygiene and its impact on infant mortality from 1875 to 1925 and implication for today: a review.J Food Prot. 2018; 81: 1713-1722Crossref PubMed Scopus (13) Google Scholar Mid-19th century infant mortality in many nations occurred in excess of 200 per 1000 livebirths per year. Pasteurisation saved the day. Now, taking the process a step further, ultra-pasteurisation at very high temperatures for very short times is widely practised in Europe. As a result, shelf life, even without refrigeration, could extend for up to 6 months or more. Consequently, without any hesitation, the heat treatment of liquid food products, including eggs, remains Pasteur's most significant legacy as a service to the world. Gerald Geison offers that "pasteurization is, indeed a symbol of his scientific life; it recalls the part he played in establishing the theoretical basis of germ theory, and the phenomenal effort that he devoted to making it useful to his fellow men. It reminds us also of his oft-repeated statement: 'There are no such things as pure and applied science—there are only science, and the applications of science.'"2Geison GL The private science of Louis Pasteur. Princeton University Press, Princeton, NJ1995Google Scholar In summary, Pasteur was a prodigious researcher. He accomplished a great deal in his lifetime without a medical degree. Yet, he consistently downplayed assistance from colleagues in his studies. Also, he did not report findings appropriately or in a timely manner. The key to ascertaining accuracy of activity is through study of Pasteur's laboratory notebooks that have only in recent years become available to historians. The notebooks are written in longhand script and for the most part are single spaced. Extensive contemporary study has helped identify myths and misunderstanding of Pasteur's accomplishments as detailed in the biography by Geison. He validates many of Pasteur's accomplishments, not as luck or serendipity, but summarised in Pasteur's famous maxim, "chance favors only the prepared mind".2Geison GL The private science of Louis Pasteur. Princeton University Press, Princeton, NJ1995Google Scholar Nevertheless, myths and reverence for Pasteur during his lifetime have persisted. Geison offered a quote by Auguste Lutard from Pasteur et la rage, 1887, "In France, one can be an anarchist, a communist or a nihilist, but one cannot be an anti-Pastorian. A simple question of science has been made into a question of patriotism." A more complete myth-dispelling paper on Pasteur is offered in a recent review by Cavaillon and Legout3Cavaillon JM Legout S Louis Pasteur: between myth and reality.Biomolecules. 2022; 12: 596Crossref PubMed Scopus (6) Google Scholar for readers desiring more such information. A chronological outline of Pasteur's major research interests is found in the panel.PanelChronological outline of Pasteur's major research interests6Geison GL Louis Pasteur.in: Gillispie CC The Dictionary of Scientific Biography. vol 10. Charles Scribner's Sons, New York, NY1974: 350-416Google Scholar•1847–57, crystallography: optical activity and crystalline asymmetry•1857–65, fermentation and spontaneous generation: studies on vinegar and wine•1865–70, silkworm diseases: pébrine and flacherie•1871–76, studies on beer production: further debates over fermentation and spontaneous generation•1877–95, cause and prophylaxis of infectious diseases: anthrax, fowl cholera, swine erysipelas, and rabies •1847–57, crystallography: optical activity and crystalline asymmetry•1857–65, fermentation and spontaneous generation: studies on vinegar and wine•1865–70, silkworm diseases: pébrine and flacherie•1871–76, studies on beer production: further debates over fermentation and spontaneous generation•1877–95, cause and prophylaxis of infectious diseases: anthrax, fowl cholera, swine erysipelas, and rabies I declare no competing interests. I was President of the American Veterinary Medical History Society (2011–12; 2018–19).